Breaking Teeth on Starter Pinion

I have a stock EVO on a '99 FLSTC. Recently,, at about 13,000 miles,, after never having any problem with my starting system (other than a new battery a couple of years ago),,, my starter began to spin instead of engaging. After learning that this was a symptom of a faulty starter clutch,,,, I removed the primary,, the jackshaft bolt, and then the starter. The jackshaft assembly was never removed from the case. I had my neighborhood alt/starter shop go thru the starter and repair the starter clutch. I re-assembled all on the bike,, making sure the jackshaft bolt washer was properly inset in the keyway groove. Everything worked fine for a couple of weeks of starting and riding daily. Then,, one morning when pushing the starter button,, there was a loud clanking noise in the primary side . There had been no indication of there being a problem on any of the previous starts the day before. After a couple of tries (with no change to the noise),, I removed the primary cover to find 2 broken teeth on the starter pinion gear. I found the 2 (whole) teeth lying inside,, cleaned all involved and replaced the pinion gear with a new one. All was fine once again,,, until about 3 weeks later (again, riding every day),,,,,,, it again has broken the teeth on the pinion gear. The problem is one that develops with previous great starts everytime,, and then all of a sudden breaking the teeth. As I said previously,, this is a stock compression evo. Any input of what may be causing this would be appreciated. Did I possibly,,, or my starter repairman possibly do something wrong? Or is there something else that may need to be looked at?
Thanks

Unfortunately, it is an all too often occurrence on the late model starter setups.

I would check for binding on the outer bushing and the jackshaft. Also, make sure the inner and outer bushings are getting oil. One thing I would do is make sure that the splines on the inside and on the coupler go fully together.

https://www.directparts.com/static/articles/motorcycle_gears.htm